Joint arrangement in connection with a wood element blank

ABSTRACT

The invention relates to a joint arrangement in connection with the manufacture of a wood element blank, especially a wood board blank or a wood beam blank, in which arrangement the wood element blank is arranged to be formed of several blank battens (1-4) that are arranged to be interconnected with an adhesive, whereupon each blank batten (1-4) is formed to have at least partly substantially triangular cross section, so that it may rest on at least four adjacent blank battens, and that the apex of the triangular part of each blank batten (1-4) remains inside the wood element blank. In order to improve the yield and the strength properties, each blank batten (1-4) is formed with substantially radial cleavings, so that the pith of the wood remains at the apex of the triangular part of the blank batten.

The invention relates to a joint arrangement in connection with themanufacture of a wood element blank, especially a wood board blank or awood beam blank, in which arrangement the wood element blank is arrangedto be formed of several blank battens that are arranged to beinterconnected with an adhesive, whereupon each blank batten is formedto have at least partly substantially triangular cross-section, so thatit may rest on at least four adjacent blank battens, and that the apexof the triangular part of each blank batten remains inside the woodelement blank.

Such wood element blanks are at present very well known in differentfields of technology. However, the previously known wood boards haveoften been manufactured in such a way that each blank batten only restson two adjacent blank battens. The problem of such a board is, however,that for example its strength and processing properties are not the bestpossible. Another drawback is that the pith of the wood will often be onthe surface of the board, wherefore the end product is not the bestpossible aesthetically. A further drawback of the prior art is that ithas not always been exactly simple to provide for example curvedsurfaces. Examples of such arrangements are described in the PCT patentapplication WO 89/04747 and in European Patent Application 0 027 488.

Board arrangements wherein each blank batten rests on more than twoadjacent blank battens have also been developed in the field. An exampleof such arrangements is disclosed in German Patent 290 153. One of thedrawbacks of this known arrangement is that the pith of the wood will beon the surface of the board. Another disadvantage is the unfavourableorientation of the wood fibres. This drawback leads to problems withstrength, since wood stretches and contracts in different ways in thedirection of the fibres and perpendicularly to the fibres.

The purpose of the invention is to provide a joint arrangement by meansof which the prior art drawbacks can be eliminated. This is achievedwith the joint arrangement according to the invention, characterized inthat each blank batten is formed with substantially radial cleavings, sothat the pith of the wood remains at the apex of the triangular part ofthe blank batten.

An advantage of the invention is for example that the cracking tensionor warping tension are not significantly transferred to the board orbeam.

Therefore, the arrangement is applicable in almost all timber species.Another advantage of the invention is that the knots will be positionedat such an angle to the surface that is as advantageous as possible,i.e. perpendicularly to the surface. The aforementioned feature ishighly advantageous with respect to the appearance and the processing.Furthermore, the pith of the wood will never be on the surface, becauseif it is not completely removed during the processing it will remaininside the board. Another advantage is that each blank batten rests onseveral other battens, wherefore the end product will be highlyadvantageous, for example either straight, curved or twisted in acontrolled manner, as well as uniform in quality and more elastic inevery direction than previously. The board surfaces are systematicallyformed from the best part of the wood, and the direction of the fibresis highly advantageous with respect to stress. Additional strength isprovided by a straight and diagonal plain joint that is about 20% widerthan in the previous arrangements. Another advantage of the invention isthat it is easy to implement, whereupon the production line will besimple, rational, effective and inexpensive. Another factor contributingto faster and easier manufacture is that each blank batten fits in itsplace only the right way round. The arrangement according to theinvention can be applied both in manual and automated manufacture ofboards or beams. A further advantage of the invention is itsconsiderably higher yield compared to the prior art. Another advantageis the possibility of utilizing a considerably wide variety of rawmaterials, i.e. all kinds of timber from stacked timber to logs issuitable for raw material. A further advantage is that the blankaccording to the invention can be used in the production of severaldifferent products, i.e. the invention is highly versatile in practice.

In the following, the invention will be described in greater detail bymeans of preferred embodiments shown in the accompanying drawings, inwhich

FIG. 1 shows an advantageous example of manufacturing blank battens,

FIG. 2 shows a first board blank embodiment provided by means of thejoint arrangement according to the invention,

FIG. 3 shows a second board blank embodiment provided by means of thejoint arrangement according to the invention,

FIG. 4 shows a preferred beam blank embodiment provided by means of thejoint arrangement according to the invention, and

FIG. 5 shows in principle examples of the kind of products that can beproduced from the wood element blank according to the invention.

FIG. 1 shows an example of how the blank battens to be used in the jointarrangement according to the invention can be manufactured. As FIG. 1shows, blank battens can be advantageously prepared for example fromround small-dimension timber. FIG. 1 shows four different blank battens,denoted with reference numerals 1 to 4. The different blank battens 1 to4 are only shown as examples of typical cross-sectional shapes. It isclear that for example four similar blank battens can also bemanufactured from the wood.

As FIG. 1 shows, the yield increases substantially with respect to theprior art. As flexible blank elements, the blank battens 1 to 4 can bereasonably curved, wherefore sawing and planing waste will be minimalwith a technique utilizing a small blade.

An essential feature of the invention is that each blank batten 1, 2, 3or 4 in the board or beam is designed in such a way that it may rest onat least four adjacent blank battens. Each blank batten 1 to 4 isdesigned in such a way that at least part of the cross-section of theblank batten has a substantially triangular shape. The aforementionedtriangular shape is provided by cutting, for example sawing, the woodradially so that the pith of the wood will be at the apex of thetriangle. This is clearly visible in FIG. 1. Tensions in the wood areeliminated by means of radial cleaving in the best possible manner,wherefore cracking or twisting do not occur in a finished board or beamblank under normal uniform moisture conditions. The edge surfaces of theblank batten, formed by means of the aforementioned cleaving, arearranged together with the edge surfaces of the adjacent blank battensto form straight and diagonal adhesive surfaces, which means that theadhesive surfaces are both perpendicular to and at an angle to the outersurfaces of the board blank or beam blank, as will be shown below.

FIG. 2 shows an example of a wood board blank manufactured with theJoint arrangement according to the invention. The embodiment of FIG. 2utilizes the blank battens denoted with reference numeral 3 in FIG. 1.The blank batten which has a partly triangular cross-section, i.e. whichis wedge-shaped, is highly applicable in both automatic and manualmanufacture of a board or beam blank. Each blank batten can be fitted inplace only in the correct position, and each batten settles easily andtightly against each of its joints. The spreading of the adhesive on theblank battens constitutes fully conventional technology for a personskilled in the art, wherefore it will not be described in greater detailhere. The straight and diagonal plain joints between the blank battensare clearly visible in FIG. 2. When FIGS. 1 and 2 are compared, it canbe seen that the pith of the wood is never on the surface of the board,since it is either removed during the processing or it remains at theapex of the triangle inside the board. Therefore the board will alwayshave a first-class surface, thus providing an advantageous finalproduct.

FIG. 3 shows a second preferred embodiment of the board blank. Thisembodiment utilizes the blank battens denoted with reference numerals 1and 2 in FIG. 1. The embodiment of FIG. 3 corresponds substantially tothe embodiment of FIG. 2. The example of FIG. 3 only shows that inaddition to an even surface, the joint arrangement according to theinvention also provides for example embossed surfaces.

FIGS. 2 and 3 show that each blank batten 1, 2 or 3 in the boardembodiment is arranged to rest on four adjacent blank battens. Theaforementioned feature is shown in FIG. 2 by denoting one blank battenwith reference A. The blank batten A rests on four adjacent battens,denoted with references A1, A2, A3 and A4. The result is a very strongstructure wherein the plain joint is about 20% larger than in the priorart. A corresponding situation is shown in FIG. 3 by means of blankbatten B and the adjacent blank battens B1, B2, B3 and B4.

FIGS. 2 and 3 also illustrate, by means of lines, the principle of howfor example board blanks can be cut to produce a desired result. Thesmall beams and components required in the construction industry,beginning from door and window casings, are provided by cleaving a boardof suitable thickness, shape and length.

FIG. 4 shows an example of a beam blank formed by means of the jointarrangement according to the invention. The blank according to FIG. 4 isproduced from the blank battens denoted with reference numerals 2 and 3in FIG. 1

Exactly the same features concern the beam blank as the board blankdescribed above. In the case of a beam blank, each blank batten isarranged to rest on six adjacent blank battens. This is shown in FIG. 4by means of a blank batten denoted by reference C. The blank batten Crests on six adjacent blank battens C1, C2, C3, C4, C5 and C6. Largebeams and all boards with fibre-edge surfaces are sawn off beam blanksformed in the aforementioned manner. This is shown in FIG. 4 with dashedlines. Due to for example small lateral moisture-induced movements,boards with fibre-edge surfaces are useful as bottom plates in concreteand felt roofing and as intermediate carpets, made of spruce, in parquetindustry, among other things. In the aforementioned manner, the frameparts of spiral stairs and banisters can also be manufactured muchbetter that with the conventional technique. This is due to the factthat as it has been stated above, the final product is the best that canbe produced from wood, i.e. either straight, curved or twisted in acontrolled manner, as well as uniform in quality in every direction. Thedirections of the fibres are in practice the kind that have been foundto be the most advantageous, and when the product is strained, thefibres act as tension and compression elements.

FIG. 5 shows in principle the kind of products that can be manufacturedfrom the wood element blank according to the invention. FIG. 5 showssmall-dimension timber with a round cross-section, the blank battens D1,D2, D3 and D4 having been cut from this timber by means of the principleof FIG. 1. The blank battens D1 to D4 thus correspond in principle tothe blank battens 1 to 4 in FIG. 1. FIG. 5 also shows the location ofthe quality layers of wood, i.e. heartwood and sapwood, in blank battensand in a finished wood element blank.

The wood element blank according to the invention can be produced byadding and compressing to the edge always four blank battens D1 to D4 ata time. This provides the blank according to FIG. 5. It should be notedthat in principle the blank can be manufactured in any size. It shouldalso be noted that if the adhesive of the central joint in the blank ofFIG. 5 is left out, two thinner board blanks are provided in a simplermanner. An example of the dimensions is that utilizing round timberthicknesses with a diameter of 8 to 10 cm provides basic boardthicknesses of 3 to 22 cm. Cleaving the basic board in the manner ofFIG. 5 provides general and special-purpose boards, designed accordingto the needs of the customer, with the best possible fibre structure andwood quality for the required purpose. The quality of the surfaces, i.e.sapwood or heartwood, as well as their colour and shape can also beselected advantageously.

The places and forms of application mentioned in FIG. 5 are onlyexamples of the different possibilities of applying the invention.

The embodiments disclosed above are not intended to limit the inventionin any way, but the invention can be modified quite freely within thescope of the claims. Therefore it is clear that the joint arrangementaccording to the invention or its details do not necessarily have to beexactly like those shown in the figures, but other kinds of arrangementsare also possible. The shape of the blank battens does not have tocorrespond exactly to that shown in the figures, but the wedge-shapedpart can be sharper or more obtuse depending on the needs of eachsituation. The dimensions may also vary quite freely, as well as forexample the shapes of the part remaining on the surface of the board. Inaddition to straight pieces, curved pieces can also be formed of theboards and beams. For example the manufacture of arch-like boardelements is quite possible. Correspondingly, curved or twisted beams andother similar parts may be manufactured. It is also possible to prepare,by means of the invention, boards with several layers, for exampletwo-layer boards. In addition to round small-dimension timber, the blankbattens can also be prepared from some other wood material, for examplethe residual peeler cores of the veneer industry. It should also benoted that when blank battens are produced for example according to FIG.1, it is possible that the four blank battens to be manufacturedsimultaneously can be made directly into a one-layer or two-layer boardor beam, depending on the manner of piling.

We claim:
 1. In a wood element blank formed of several blank battensthat are interconnected with an adhesive, the improvementcomprising:blank battens formed to have a substantially triangularcross-section part, and to have surfaces of contact with at least fouradjacent blank battens; and wherein said blank battens are formed withsubstantially radial cleavings, so that the pith of the wood remains atan apex of the triangular cross-section part inside the wood elementblank.
 2. A wood element blank according to claim 1, wherein thesurfaces of contact form straight and diagonal plain joints withsurfaces of the adjacent blank battens.